Human embryonic stem (hES) cells are a unique scientific and medical resource. These pluripotent cells are self-renewing and have the capacity for differentiation into many types of cells. The potential for using hES cells in transplantation therapies for numerous diseases, including diabetes and Parkinson's disease, has been widely discussed. Despite their considerable potential, there is rather little known about the genetic regulation of human embryonic stem cells. For example, the genes and signaling pathways that control self-renewal of hES cells have not been identified. Similarly, the genes that regulate hES cell differentiation into various embryonic germ layers and specialized cells are unknown. In the absence of understanding the genetic control of hES cell self-renewal and differentiation, the experimental manipulation of hES cells, either for research or therapeutic purposes, is bound to remain in a rudimentary state. This project will characterize the transcriptional program of human embryonic stem cells and discover genes involved in their self-renewal and differentiation. The genetic program that characterizes undifferentiated hES cells will be analyzed using DNA microarrays. In addition, a gene "trap" strategy will be used to identify genes that potentially control hES differentiation into the three embryonic germ layers. The function of selected genes will be explored using conditional expression during hES cell differentiation. Four lines of hES cells will be used for these studies. They are: H1 (WA01), H9 (WA09), H13 (WA13) and HES-1 (ES01); the NIH registry number is in parentheses.